The present invention relates to an improved type of carbon-containing refractory and more specifically to burned and unburned Al.sub.2 O.sub.3 --C, MgO--C, and MgO--Al.sub.2 O.sub.3 --C refractories having improved resistance to oxidation, spalling, and corrosion, in addition to improved hot strength.
Refractories containing carbon in the form of graphite are widely used in metallurgy. When in contact with molten iron, molten steel, or slag, these refractories exhibit excellent resistance to corrosion. Since graphite itself is resistant to wetting by slag, its presence in refractories prevents the penetration of slag into the refractories. Further, because of the presence of graphite, the refractories can not be over-sintered, and therefore thermal spalling does not readily occur. This, too, contributes to the high refractoriness of graphite-containing refractories.
However, graphite is very easily oxidized by oxygen in its surroundings, which causes a graphite-containing refractory to lose its excellent characteristics. In order to obtain a refractory with good characteristics, it is extremely important to decrease the oxidation of graphite. Various methods have been proposed of increasing the resistance to oxidation of this type of refractory, but at present no satisfactory method has been found.
Japanese Patent Laid Open No. 50-69106 disclosed covering the surface of a carbon-containing molded refractory material with a nitride or carbide of silicon and further coating it with a borosilicate glass comprising boron carbide and silicon dioxide in order to prevent oxidation. However, these covering layers are not resistant to attack by molten iron, molten steel, or slag, and if worn through by chemical attack will lose their anti-oxidizing effect. Accordingly, this method is not desirable.
Another method of preventing oxidation in carbon-containing refractories is to uniformly disperse metal powder in a carbon-containing molded refractory material. Japanese Patent Laid Open No. 55-107749 disclosed adding magnesium powder, aluminum powder, and silicon powder to carbon-containing refractory bricks, and Japanese Patent Laid Open No. 54-39422 disclosed adding to carbon-containing refractories a metal powder having a greater affinity for oxygen than carbon. In the latter invention, at least one type of metal powder selected from Al, Si, Cr, Ti, and Mg is added. However, the resistance to oxidation and the hot strength of the resulting carbon-containing refractory are not fully satisfactory.